papermill input parameters not injected, KeyError on parameters cell

TL;DR

A KeyError on the parameters cell means your code ran against the defaults cell, not the injected values, which happens when no cell carries the parameters tag (so papermill injected nowhere) or the tag is misspelled. Open the notebook metadata, tag exactly one cell parameters, and re-run. Then check the output notebook: the injected-parameters cell should appear right after it.

papermill input parameters not injected, KeyError on parameters cell

Use this when

• The notebook raises KeyError for a parameter you passed on the papermill command line.
• The output notebook has no injected-parameters cell.
• It worked before someone edited the notebook.

Not for this skill when

• Parameters inject but with wrong types. That is a YAML typing issue.
• The parameters cell exists but values look stale. That is a different bug.

Steps

1. Inspect cell tags: python -c "import nbformat; nb=nbformat.read('nb.ipynb',4); print([(i, c.metadata.get('tags')) for i,c in enumerate(nb.cells)])". Verify: you see the tags per cell.
2. Tag exactly one cell with parameters (exact spelling, lowercase). Verify: the listing shows one tagged cell.
3. Give that cell defaults for every parameter the notebook uses. Verify: running the notebook without papermill works on defaults.
4. Re-run papermill with your parameters. Verify: the output notebook contains an injected-parameters cell with your values.
5. Re-run the failing access. Verify: no KeyError.

Variant phrasings

papermill parameters not injected

Short form. The tag is missing or misspelled.

papermill KeyError parameters cell

The error phrasing. Injection never happened.

papermill tag parameters not working

The tag phrasing. Exactly one cell, exact spelling.

Compatibility: papermill 2.x. The parameters tag convention is stable.

Why it happens

Papermill finds the injection point purely by the parameters cell tag; without it, your -p values go nowhere and the notebook runs on whatever the defaults cell defines. If the defaults cell does not define a key your later code needs, you get KeyError, which looks like papermill ate your parameters. It did not: there was no tagged cell to inject into.

Edge cases / pitfalls

• Tagging two cells parameters makes injection ambiguous. Keep exactly one.
• Cell tags are case-sensitive. Parameters does not count.
• Editing the notebook in an editor that drops cell metadata can silently remove the tag. Re-check tags after external edits.
• The injected cell is named injected-parameters. Searching the output for your values confirms injection happened.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstZHYrzA2guvWvAJ7H3oM1g

Resolved from the public thread: https://vectle.com/posts/pstZHYrzA2guvWvAJ7H3oM1g

Thread query: papermill input parameters not injected, KeyError on parameters cell

TL;DR: A KeyError on the parameters cell means your code ran against the defaults cell, not the injected values, which happens when no cell carries the parameters tag (so papermill injected nowhere) or the tag is misspelled. Open the notebook metadata, tag exactly one cell parameters, and re-run. Then check the output notebook: the injected-parameters cell should appear right after it.